This invention deals with the intercalation of polyvalent cations in the structure of beta double prime aluminas (BDPAs) and certain related species. This invention is also directed to methods for the intercalation of polyvalent cationic species in beta double prime aluminas, and with articles employing the modified double prime aluminas thus prepared. Devices which employ the fluorescent or phosphorescent character of certain of these modified materials together with devices which exploit the ability of certain of these materials to undergo laser emissions are also contemplated by the present invention.
Intercalation of monovalent and certain divalent cations in both beta alumina and beta double prime alumina is known. See in this regard, "Fast Ionic Transport in Solids", Farrington et al., Science, Vol. 204, pp. 1371-1379 (1979). Such cations of sodium, potassium, silver, copper, lithium, and certain other elements have been known to be conducted into and out of both of these materials. The conductivity of a cation in different alumina lattices depend on the energy of activation for the individual processes which, in turn, is related to an ion's size and its tendency to bond to oxygen atoms in the conduction planes of the various materials. Thus, for beta alumina, the energy of activation increases with increasing ionic size from sodium to rubidium. Increasing difficulties in intercalation are expected for beta alumina as larger ions are considered. It has been believed that similar relationships are extant for magnetoplumbites as well as for beta double prime aluminas.
The preparation of high conductivity solid electrolytes for divalent cations from beta double prime aluminas has been disclosed. See "Divalent Beta" Aluminas: High Conductivity Solid Electrolytes for Divalent Cations", Farrington and Dunn, Solid State Ionics, Vol. 7, No. 4, pp. 267-281 (1982). It was found that divalent cations could readily diffuse or intercalate into beta double prime alumina leaving the divalent ions intercalated therein. It was observed that divalent cations diffuse very slowly in beta alumina, however. While it was found that divalent cations may diffuse into beta double prime alumina to form intercalated structures, it has been assumed that cations having three, four, and higher positive charges, i.e. trivalent, tetravalent and higher cations (hereinafter collectively referred to as polyvalent cations) would not be capable of penetrating any of the alumina lattices including the beta double prime alumina structure. This assumption was supported by prior experimental data. Thus, for example, while the conductivity of sodium cations in beta double prime alumina is approximately 10.sup.-2 ohms.sup.-1 cm.sup.-1 at 25.degree. C., the conductivity of (divalent) barium ions is approximately 10.sup.-7 ohms.sup.-1 cm.sup.-1 at 25.degree. C. Even though these conductivities are substantially higher than those exhibited in beta alumina and magnetoplumbite, it has been generally anticipated that conductivity of trivalent cations (not to mention tetravalent cations) in any of the aluminas, including beta double prime alumina, would be vanishingly small or nonexistent.
In view of the foregoing considerations, the preparation of aluminas having polyvalent cationic species intercalated therein has not been heretofore attempted. Rather, others have attempted the preparation of, for example, lanthanide aluminate-type materials through high temperature synthesis or recrystallization. See "Preparation, Structure, Optical and Magnetic Properties of Lanthanide Aluminate Single Crystals (LnMAl.sub.11 O.sub.19)", Kahn et al., Journal of Applied Physics, Vol. 52, No. 11, pp. 6864-6869 (1981); "A Survey of a Group of Phosphors, Based on Hexagonal Aluminate and Gallate Host Lattices", Verstegen, Journal of the Electrochemical Society, Vol. 121, No. 12, p. 1623-1627 (1974); "Optical and Structural Investigation of the Lanthanum .beta.-Alumina Phase Doped With Europium", Dexpert-Ghys et al., Journal of Solid State Chemistry, Vol. 19, pp. 193-204 (1976); and "Eu.sup.2+ Luminescence in Hexagonal Aluminates Containing Large Divalent or Trivalent Cations", Stevels et al., Journal of the Electrochemical Society, Vol. 123, No. 5, pp. 691-697 (197). See also " Properties of .beta.-Alumina Doped With Cerium", Kennedy et al., Journal of Solid State Chemistry, Vol. 42, pp. 170-175 (1982); and "The Relation Between Crystal Structure and Luminescence in .beta.-Alumina and Magnetoplumbite Phases", Verstegen et al., Journal of Luminescence, Vol. 9, pp. 406-414 (1974).
Other publications dealing with cationic substitution in beta alumina or magnetoplumbite type materials include "X-Ray Diffuse Scattering from Alkali, Silver and Europium .beta.-Alumina", McWhan et al., Physical Review B, Vol. 17, No. 10 (1978); "Mn.sup.2+ and T1.sup.+ Luminescence in .beta.-Aluminas", Verstegen et al., Journal of Luminescence, Vol. 10, pp. 31-38 (1975); "Effects of Defects on the Quantum Efficiency of Eu.sup.2+ -Doped Aluminates with the Magnetoplumbite-Type Crystal Structure", Stevels et al., Journal of Luminescence, Vol. 14, pp. 147-152 (1976); "Eu.sup.2+ Mn.sup.2+ Energy Transfer in Hexagonal Aluminates", Stevels et al., Journal Of Luminescence, Vol. 14, pp. 207-218 (1976); and "Luminescence of (Sr, Ce)-Hexa-Aluminates", Alexander et al., Abstract No. 609, Extended Abstracts 83-1, Electrochemical Society Meeting San Francisco, Calif., May, 1983.